TOCHIGI, Japan--Nestled among the rice paddies 125 miles north of Tokyo sit Honda Motor's research and development departments. Among those facilities is a high-banked oval test track. And on that oval this weekend, I drove the company's latest hydrogen fuel-cell car, the FCX Concept. I couldn't get it past 91 mph, with three passengers. Others in the group, with only two in the car, saw 94 mph.

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So much for any doubt over a fuel-cell car being able to keep up with traffic in the States.

This latest FCX by Honda is a major leap forward toward the viability of the hydrogen-powered family car. For one thing, the four-door FCX easily seats the typical family of four, can squeeze a fifth and carry some luggage as well.

The key to the new car is its fuel-cell stack. The stack uses hydrocarbon membranes and stamped steel plates encased in an aluminum box. The design minimizes the effects of heat and, more importantly, helps the water produced during electricity production to drain quickly. Low-temperature startup has been improved, with the car ready to start and run at ambient temperatures as low as 22°F. The fuel-cell stack also has a low profile and is mounted in the car's center tunnel--a configuration that allows room for a lithium-ion battery pack as an auxiliary power source as well as two 5000-psi hydrogen storage tanks. The car also has a small, transversely mounted coaxial motor which is narrow enough to fit beneath the short hood. The motor is rated at 127 hp and 189 lb/ft of torque.

And, as we proved to ourselves, it works just fine. The car looks good, accelerates smoothly and quickly past all legal speed limits and is comfortable for front and rear seaters.

Moreover, the FCX Concept will become the basis for a hydrogen fuel-cell car on the horizon for sale in the U.S. and Japan. In fact, according to Honda President and CEO Takeo Fukui, the car will be on the market--in limited numbers--in 2008.

Also due in "the next three years," company officials say, is Honda's clean diesel. Like other modern diesel engines designed to meet the stringent clean-air standards, Honda relies on both a particulate trap to remove hydrocarbons from the exhaust as well as urea treatment of the exhaust to all but remove NOx.

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Reducing NOx has been the big stumbling block for all auto engineers and, as we've seen recently with DaimlerChrysler's Bluetec and AdBlue, adding urea, or ammonia, to the exhaust stream does the trick. However, Honda's engineers have developed a special two-layer catalytic converter which essentially produces its own ammonia, eliminating the need for a special storage tank and regular refills.

One layer of the converter adsorbs NOx from the exhaust and coverts part of it into ammonia, which the other layer adsorbs and uses to treat the remaining NOx. To make the catalyst work, the engine runs alternately lean burn and rich burn. During lean burn, the NOx adsorbent in the cat's lower layer grabs the NOx from the exhaust. The engine's control unit then switches to a richer mixture, with the trapped NOx and rich exhaust's hydrogen reacting to produce ammonia. The cat's outer layer adsorbs the ammonia, and when the engine returns to lean burn, the ammonia in the cat's upper layer reacts with the NOx in the exhaust and reduces it to nitrogen. No fuss, no mess.

The car I drove that had the system--an Accord--was peppy and fast. But the engine itself was noisier and rougher (particularly at idle) than other currently available diesels. Honda's engineers admitted that there was still some refinement to be done to the drivetrain, and no one from Honda would say which vehicles will have diesel power, adding only that they would "have it soon."

Interestingly, the engineers are also working on a combustion pressure sensor system that will automatically adjust for the widely different cetane ratings of available diesel fuel. No word on when that will be ready.--Don Chaikin

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